has journeyed to the center of the Earth to see what it is like. However, scientists
using seismic waves have developed models showing what the Earth is made of
and the thickness of the different layers.
Click on the labels to learn more about Earth's layers.
The crust is the Earth’s thin outer rind. It accounts for only 0.4
percent of the Earth's mass. The boundary between the crust and the mantle
is called the Mohorovicic Discontinuity or MOHO for short. There are two types of crust:
1.) The continental crust is 30-70 kilometers thick. It is made of all three
types of rocks; igneous, sedimentary, and metamorphic. Most of these rocks
are made of 60 to 70 percent silica (or quartz).
2.) The oceanic crust is only six kilometers thick. It is composed of layers
of igneous rocks that contain 50 to 60 percent silica. These rocks have more
iron and magnesium than those in the continental crust. Magma that erupts
onto the ocean floor cools quickly, forming pillow lava. Over thousands of
years, the remains of shells and microscopic plants and animals rain down,
blanketing the deep ocean floor under a layer of sediment.
The upper mantle is 400 kilometers thick. It is weaker than the rest of the
mantle and bends and flows under pressure. Like the lower mantle, the upper
mantle is made up of minerals rich in iron, silica, magnesium, and oxygen.
The solid lower mantle is 2,500 kilometers thick. It is composed of minerals
rich in iron, silica, magnesium, and oxygen. Together, the upper and lower
mantle make up two-thirds of the Earth's mass.